Deep etching lithographic plate



Patented Apr. 13,,1943.

UNITED STATES PATENT" 1 OFFICE I near fiomncrirfifeflkmc mm I PhilipZeiger, New York, N. Y.

No Drawing. Application February 25, 1942,

I Serial No. 432,239

1 Glaim. (cur-41,5)

This invention relates to improvements in theart of deep etchinglithographic plates.

In the common procedure of making deep etch lithographic plates, theplate is first freed of oxide fllm by treatment with-counteretchsolution, after which the plate is coated with alightsensitivedichromated gum solution and the desired design is then photographicallyexposed on the sensitized coating, thereby hardening the portions of thecoating exposed to the action of light. other areas which it is. notdesired to have appear in the print ultimately made from the plate, arestopped out with shellac solution or other appropriate material. Theexposed design is then developed with -a suitable developing solutionand the spent developing solution is re moved with simultaneous removalof the unhardened portions of the gum coating, after which the plate isready for deep etching. The etching of the plate is then accomplished bytreating the uncovered portions thereof with a suitable etchingsolution, afterwhich the plate is washed with water-free denaturedalcohol to remove the etching solution as well as the stopout shellac.Following the washing operation, the plate is dried of all alcohol,after which a coating of laquer is applied evenly and thinly over itsentire surface. Next, the plate is coated with developing ink and dustedwith powdered talc. Following this, the hardened gum stencil, togetherwith the developing ink adhering thereto is removed by scrubbing withwater while the developing ink remains on the etched portion of theplate. .After drying, the plate is ready for use. This procedurerequires "a considerable quantity of alcohol for the purpose of removingthe stop-out shellac and thoroughly cleaning the plate of all developingand etching solution.

An object of this invention is a deep etching technique for producinglithographic plates which eliminates the use of alcohol, therebyeiiecting a substantial reduction in expense, as well as elim-. inatingany difliculty arising from a shortage of alcohol.

According to the present invention, a lithographic plate to be deepetched is first counteretched and then coated with light-sensitivedichromated gum solution in the usual manner and is photographicallyexposed to the desired design as heretofore. Instead of stopping out theunchromated gum coating unhardened by exposure to light are immediatelyremoved from the plate The unexposed border of the plate and through theuse of suitable developing solution as formerly. After the developingstep, the uncovered portions of the plate are treated with etchingsolution as formerly except in the absence of stopout medium. Followingthe etching operation, the plate is thoroughly rinsed in hot water(approximately boiling temperature) thereby removing the developing andetching solutions, as well as removing the hardened or light-exposedportions of the dichromated gum coating except for a very thin filmadhering to the portions of the plate corresponding to the exposedportions of the dichromated gum coating, which film inherently adheresto the plate. The major portion of the rinsing operation is preferablyeflected in a. tank of hot water followed by treating the plate withrunning water. The plate is then immediately dried preferably byblotting with clean news stock or water-leaf blotting paper and changingthe paper two or three times. The border and undesired portions are nowstopped out with regular desensitizing plate etch which is soluble inwater. After the drying of the stop-out medium, the entire plate islacquered as formerly and dried with the lacquer coating being appliedevenly and thinly. On the surface of the dried lacquer, deep etch ink isapplied and the ink film dusted with asphaltum if desired. Followingthis treatment, the plate is subjected to running water which washes ofithe lacquer together with the adhering ink from the portions of theplate coated on the parts corresponding to the light-hardened portionsof the dichromated gum coating with the previously mentioned film aswell as the stop-out medium while leaving the ink on the etched portionsof the plate. The lacquer and excess ink may also be removed byimmersing the plate in a tank of warm, but not hot, water and wiping oilwith absorbent cotton. Following the drying of the plate subsequent tothe operation of removing the excess ink and lacquer, the plate is readyfor 'use in the usual manner.

The technique above described is carried on without the use of alcohol.The alcohol can be dispensed with due to the fact that shellac is notused as the stop-out medium. Instead of using shellac as the stop-outmedium, water-soluble plate etch is used as the stop-out medium afterthe etching step so that it is not subjected to the washing operationfollowing the completion of the etching step but is applied just priorto the application of lacquer.

I claim:

The method of deep etching a plate which consists in coating the samewith light-sensitive dithe entire surface or the p te including said sop-o m coating said lacquer mm with ink and washing of! said stop-outmedium together with lacquer and adhering ink from the 5 unetchedportions or the plate while leaving ml:

in the etched portions of the plate.

PHILIP ZEIGER.

